Consumer demand has been responsible for the single handle mixing valve for tub and shower installations becoming common in the marketplace. With the passage of time, the single handle mixing valve has undergone design changes to permit large volumetric flows of water through the valve (especially in hotel and other commercial establishments such as gymnasiums, apartments and condominiums) with the end result being that some form of pressure balancing between the hot and cold water supplies feeding the mixing valves has become essential. Without the incorporation of a suitable pressure balancing mechanism in the mixing valves, the operation of such high pressure, high flow volume valves in hotels and gymnasiums could lead to serious injury to the user in the event of a sudden pressure change in the hot or cold water supply to the mixing valve.
Most governing codes require that any tub or shower mixing valve include some kind of a pressure balancing mechanism which is capable of responding to abrupt changes in pressure of the hot and cold water supplies within a very short time to restore the balance of the output flows of hot and cold water to the same proportion as they were before the pressure fluctuation occurred.
Because such mixing valves must fit into a confined space, compromises must be made between performance of the valve and the space required for valve in the plumbing installation. Most prior art valves use a spool type poppet valve mechanism to provide a pressure balance in the hot and cold water supplies feeding the valve. Some of the prior art pressure balancing mechanisms are sufficiently complex as to require the services of sophisticated service personnel to overhaul, dismantle or repair such prior art valves.
It will be immediately apparent that a single handle mixing cartridge valve of a compact size which is capable of controlling large flows of hot and cold water in an inverse manner according to pressure fluctuations in the inlet supplies is a most desirable item for the plumbing industry. If the above valve could comprise a housing containing a single cartridge that was easily removed for repair or replacement by untrained service personnel, the valve is all the more desirable.